Search

Chemical and electrical thrusters are generally utilized to control the attitude and orbit of spacecraft in aerospace. When they are firing, the exhaust expands into the vacuum environment, known as the vacuum plume. The plume flow can collide with spacecraft surfaces due to sufficient expansion, exerting adverse effects on the spacecraft, such as heating load, force/torque, contamination, and sputtering. Therefore, it is vital to investigate the vacuum plume to ensure the function and safety of the spacecraft. This review introduces the ground test and numerical simulation methods of the vacuum plume for chemical and electrical thrusters. The vacuum environment, invasive, and non-invasive (optical) measurements of the ground test are concluded. Numerical simulation of plume flow and its effects is exampled. The hybrid CFD-DSMC (computational fluid dynamics and direct simulation Monte Carlo) algorithm is employed to simulate the gas plume flow spanning continuum and transitional and free molecular flow regimes for chemical thrusters. By contrast, the PIC-DSMC (particle-in-cell plus direct simulation Monte Carlo) algorithm is used for the plasma plume flow containing charged particles exhausted by electrical thrusters. Moreover, the topics of fast prediction of the vacuum plume, plume–surface interaction, and plume–Lunar/Mars regolith interaction are proposed for future research.

In this paper, an improved discrete sliding mode control (SMC) is investigated for a hypersonic vehicle (HV) cruise control system under packet dropouts. Packet dropouts are common faults in networked control systems (NCS) of HV. The controller designed consist of a discrete SMC controller and a state feedback compensator. The state feedback compensator is designed based on the HV asynchronous dynamic model under Lyapunov theory to restrain the influence of the data packet dropouts, improve the tracking performance and anti-fault robustness. Set the HV system with state feedback as an augmentation system. A discrete SMC system is established for the augmentation system to achieve the target trajectory. We verify the discrete SMC approach in the cruising flight. A simulation example supports the theory.

In order to solve the problem that manipulators can only move in a fixed trajectory in common industrial production at present, we propose a monocular visual positioning method based on artificial beacons, combining visual position technology with the movement of manipulators to complete the reliable path planning of manipulators. When it comes to practicability, the traditional point pair-matching method is equipped with robust factors, to increase the reliability. We adopt a linear predict algorithm and ROI (region of interest) in the solving of PnP (Perspective-n-Point) to ensure the real-time performance and improve the robustness. Finally, the reliability is verified by experiments, which provides theoretical basis and practical reference for the path planning of manipulator based on artificial beacons.